Sterling has hit a fresh 31-year low against the US dollar as investors fretted over the prospect of a 'hard Brexit' following Britain's vote to leave the European Union.

The pound fell to as low as $1.2623 at one stage and €1.13 against the single currency on another brutal day.

The slump follows Theresa May's pledge this week to trigger Article 50 by March next year – paving the way for a so-called 'hard Brexit' that would pull the UK out of the single market as well as the EU.